question for ip packet

question for ip packet

[梁红军]

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  the following is the description about ppp in the Readme of linux PPPD:          
   the kernel module assembles/disassembles PPP frames, handles error
detection, and forwards packets between the serial port and either the
kernel network code or the user-level program pppd.  IP packets go
directly to the kernel network code.  So once pppd has negotiated the
link, it in practice lies completely dormant until you want to take
the link down, when it negotiates a graceful disconnect.
 question:
         1.after  pppd has negotiated the link ,what it tell information to  the kernel network ppp code ,
        which  make kernel  transmit  IP packets directly?
         2.  where to receive the IP packets from ppp kernel ?  how to know the ip packet come from not other 
        device but PPP?
 
 

	

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Re: question for ip packet

[James Cameron]

On Thu, Apr 24, 2008 at 10:41:00AM +0800, ?????? wrote:
> 1. after pppd has negotiated the link, what it tell information to the
> kernel network ppp code, which make kernel transmit IP packets
> directly?

Briefly, in function tty_establish_ppp() in sys-linux.c, an ioctl(2)
syscall sets the TTY into PPP discipline (N_PPP).  Once the interface is
up, the kernel transmits network packets through the PPP link.

> 2. where to receive the IP packets from ppp kernel?  how to know the
> ip packet come from not other device but PPP?

I don't understand.  It is very clear the packets are from the PPP link
because they can be captured from the new network interface.

-- 
James Cameron                         http://quozl.netrek.org/
HP Open Source, Volunteer             http://opensource.hp.com/
PPTP Client Project, Release Engineer http://pptpclient.sourceforge.net/